Method for relieving hydrostatic pressure in oil recovery from wells



METHOD FGR RELEEVHNG HYDRUSTATIC PRES- URE EN 031. REVERY FRUM WELLS Dolores Floyd Bloom, liaiterstield, Califl, assignor to Aircushion Patents Corporation, Bakersfield, (Caiih, a

corporation of iCalifornia No Drawing. Filed Aug. 25, 196i), Ser. No. 51,797 2 Claims. ((3l..l66 43) My invention relates to a method for improving the efiiciency of oil and gas recovery operations which require that an earth formation be relieved of the hydrostatic pressure of drilling mud or water so that oil present in the formation may be recovered.

My improved method is useful both in situations in which the initial gas pressure is insuflicient to permit recovery of oil present in a formation and in secondary recovery operations employed when the gas pressure present in an oil bearing earth formation has fallen to a level insufficient to permit recovery of the oil present.

It is also useful in connection with de-waxing operations in which it is desired to increase the permeability of an oil or gas bearing earth formation by washing the formation with liquid detergents and thereafter removing the detergents, together with dissolved or suspended material, from the well.

When an oil or gas well is drilled by conventional methods, a casing is set against the wall of the well as the drilling progresses and drilling mud is circulated downwardly through a drill string disposed within the casing and upwardly between the drill string and the easing to carry earth and rock displaced by the drill up and out of the well. When an oil or gas bearing earth formation is encountered in the course of such an operation, tubing, open at its lower end, is substituted for the drill string within the casing to conduct the oil or gas to the surface. Frequently, however, the hydrostatic pressure of the drilling mud between the tubing and the casing, which is also open at its lower end, will inhibit the flow of fluids from the formation, and it becomes necessary to remove at least a portion of this drilling mud in order to bring oil or gas to the surface. This has conventionally been accomplished by swabbing the well; that is, by mechanically lifting successive batches of drilling mud out of the well.

Swabbing has likewise been found necessary when liquid detergents have been injected into a well to remove wax deposits and the like or when acidizing is employed to increase the porosity of an oil or gas bearing earth formation. Such washing or acidizing agents, together with the dissolved or suspended material removed from the formation by their application, must, of course, be removed from the well, and swabbing has heretofore been the most convenient way to effect such removal.

According to my invention the removal of fluids such as drilling mud, washing fluids and the like from a well is accomplished solely by the application of gas pressure at the surface of the ground alternately within the up er portion of the tubing and the upper portion of the casing, while observing the outflow of liquid at the surface produced by the application of such gas pressure and switching the gas pressure from the tubing to the casing and vice versa just as the liquid outflow becomes minimal or ceases. By repeatedly alternating the application of gas pressure between the tubing and casing in this manner, a pendulum-like action of the body of liquid within the casing and the tubing is induced and successive discharges thereof through the tubing and easing, alternately, are eifected until the gas pressure within the well finally exceeds the hydrostatic pressure of the remaining drilling mud or other liquid, and a flow of oil or gas, or both, to the surface ensues, or at least until 3,019,839 Patented Feb. 6', 1962 recovery of oil from the well bore by pumping.

in carrying out the method of my invention, a high pressure source of gas, such as nitrogen, at a pressure of 1000 to 5000 pounds per square inch, is connected through conventional valves to tubing extending from the surface of the ground to adjacent the oil or gas bearing stratum of a liquid filled well. The same or a similar source of gas is also connected through conventional valves to the space between the casing and the tubing of the well.

The valves in the connection between the gas source and the tubing are 'then opened to permit gas to flow into the tubing the upper end of which is otherwise gastight, and beneath the main body of liquid in the well; the valves between the gas source and the space between the casing and tubing remaining closed. Liquid is permitted to flow, however, through an additional valve from the upper end of the casing to a sump; the upper end of the casing being otherwise gas-tight. During this phase of the operation, gas entering the well through the tubing will lift the body of liquid between the tubing and the casing, causing an outflow of fluid from the upper end of the easing into the sump. This outflow is monitored and will be observed to gradually decrease in volume, and it will finally cease.

As the monitored outflow becomes minimal, or immediately upon its cessation at the latest, the valves connecting the tubing to the'gas source are closed, other valves connecting the tubing to the sump are opened, and the valves connecting the space between the tubing and the casing to the gas source are opened. During this phase of the operation, the body of liquid lifted during the first phase, but remaining in the space between the tubing and the casing, falls toward the bottom of the tubing and is accelerated by the inflow of high pressure gas at the upper end of that space. So moving, the liquid proceeds upwardly through the tubing and an outflow of liquid from the upper end of the tubing into the sump ensues. This outflow is also monitored and will likewise be observed to gradually decrease in volume, and it will finally cease.

As this monitored outflow becomes minimal, or im mediately upon its cessation at the latest, the valve from the tubing to the sump is closed, the valve from the tubing to the gas source is reopened, the valve from the casing to the gas source is reclosed, and the valve from the casing to the sump is reopened.

In this repetition of the first phase of the operation, the body of liquid remaining in the tubing falls, accelerated by the gas pressure above it, and another outflow of liquid from the upper end of the casing to the sump will be observed which will gradually decrease in volume and finally cease, as before.

At the same point in this phase as before, the valves are again reset to the conditions pertaining in the second phase of the operation, and the successive phases are alternated preferably until an outflow of oil or formation gas is observed at the top of the well. The tubing is then connected, through a conventional gas trap to the storage reservoir.

It has been found that by employing the method of my invention it is' possible to remove a volume of liquid from a well in one or two hours, the removal of which by swabbing would require several days. Furthermore, by employing an inert gas such as nitrogen, exothermic reactions are avoided which would otherwise be dangerous in the case of removal of acidizing solutions and all risk of detonation of air and gas mixtures under the high pressures pertaining is likewise eliminated.

I claim:

1. A method of recovering fluids from an earthbore 0 t penetrating a fluid bearing formation and containing substantially coaxially disposed tubing and a casing between which a hydrostatic head bears upon the formation, in-

cluding the step of inducing a pendulum-like action of the body of liquid extending into the casing and the tubing by repeatedly alternating the steps of introducing gas at the surface of the ground between the casing and tubing under pressure sufficient to discharge a portion only of the liquid of said hydrostatic head from the opened upper end of said tubing and then introducing gas into the tubing at the surface of the ground under pressure sufficient to discharge a portion only of the liquid of said hydrostatic head from the opened upper end of said casing; the alternation between said steps being effected in timed relation with the minimalization of the liquid flow from the opened upper ends of said tubing and said casing, respectively.

2. A method according to claim 1 in which the gas 5 introduced under pressure is nitrogen.

References Cited in the file of this patent UNITED STATES PATENTS 10 1,740,039 Rubel Dec. 17, 1929 2,120,132 Hawkins June 7, 1938 2,310,001 Haddock Feb. 2, 1943 2,786,652 Wells Mar. 26, 1957 2,808,887 Erwin Oct. 8, 1957 

